Two parallel tunnels will connect the cities of Howrah and Kolkata, located on either side of the river Hooghly, by the end of July.
Remember the awesome feeling you got while passing through long tunnels during train journeys?
Now, something more awesome and cutting-edge is coming our way!
An underwater metro tunnel!
Seems straight out of a futuristic sci-fi film, right?
Well, work using a huge Tunnel Boring Machine (TBM) has already begun on the bed of the Hooghly river. There will be two parallel tunnels that will connect the cities of Howrah and Kolkata, located on either side of the river, by the end of July.
The tunnels are being dug at a depth of 30 metres below the earth’s surface and 13 metres below the riverbed.
The 520 metre tunnels under the river will connect Salt Lake Sector V in Kolkata to the Howrah Maidan across the river, being elemental in the ₹8,900 core East West Metro project.
Out of the 16.6km East West Metro route, the tunnels will pertain to a 10.8km underground stretch, along with an elevated corridor that will stretch to 5.8km.
“As per our optimistic estimate by the end of May or the first week of June this year, the first under-river tunnel of India will be complete. One tunnel-boring machine is already under the water, and the second machine will also start working by the end of May. Both the tunnels will be complete by July,” Satish Chandra, managing director of the Kolkata Metro Railway Corporation Limited (KMRCL), told The Hindu.
According to Satish, who is also assistant general manager, Eastern Railways, two TBMs cannot work at the same time due to the nature of the soft clay soil under the riverbed.
“One machine goes ahead and the second follows. They cannot work together for various technical reasons. For instance, the ground movement will be very high if they work simultaneously,” he added.
Employing about 250 people at the site of tunnelling 24×7, a thick layer of concrete is used to seal the tunnel, with the intention of preventing disasters like the collapsing of earth along with water seepage: one major concern for the engineers working on any water tunnel.
With the tunnelling and construction of East West Metro Project in full swing, there, however, have been a few glitches that require to be overcome. The digging by the German-made TBM machines led to cracks appearing in the Howrah District Library.
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After this, KMRCL authorities had to be very cautious when the tunnelling reached near Colvin Court, which is a 94-year-old railway building serving as residential quarters for railway staff, currently.
“The protective measures subsequently taken by the engineers included widening the foundation of the building and grouting of the soil,” the authorities told The Hindu.
Another concern faced by the East West Metro Project is the threat of damaging three heritage buildings that lay well within the vicinity of the Metro tunnels.
While according to the existing rules, construction and mining operations are prohibited within 100 meters of protected monuments — the Currency Building, an Italian structure that served as one of first banks of the country, is around 24 metres away from the metro’s alignment, and the Beth-El and Maghen David Jewish synagogues are within a distance of about 17 metres and 9.8 metres respectively.
Union Minister of State for Heavy Industries Babul Supriyo, who inspected the project, expressed hope to The Hindu that that the last hurdle would be cleared soon, after the issue was raised by the Archaeological Survey of India, wherein an expert committee from the IIT Kharagpur, was constituted to look into the matter.
We wish the project will be completed by surpassing all the hurdles, connecting the two cities of Howrah and Kolkata and give the metro users a whole new experience of commuting in underwater tunnels!